In a typical organic electroluminescence device (OLED), a pair of electrodes (an anode and a cathode) sandwich one or more layers comprising of a hole injection material, an emission material (with either fluorescent or phosphorescent material), and an electron transporting material. These materials are organic. Into the organic layer(s), holes and electrons are injected from the anode and the cathode, respectively. Thus, excitons form within the emission material, and when the excitons fall to the ground state the organic layer, and hence the organic luminescence device, emits light.
According to the first study by Eastman Kodak Co. (“Appl. Phys. Lett”, vol. 51, pp. 913 (1987)), an organic electroluminescence device, that comprised a layer of an aluminium quinolinol complex (as a combined electron transporting and luminescent material) and a layer of a triphenylamine derivative (as a hole transporting material), resulted in luminescence of about 1,000 cd/m2 under an applied voltage of 10 V. Further studies by Baldo et al. revealed a promising OLED using phosphorescent material as a dopant. The quantum yield of the phosphorescent OLED was significantly higher (U.S. Pat. No. 6,830,828). These systems may be referred to as small molecule OLEDs (SMOLEDs).
In addition to the above-mentioned OLEDs, a polymer based organic electroluminescent device (PLED) using a conjugated polymeric material, has been reported by a Cambridge University group (Nature, vol. 347, pp. 539 (1990), U.S. Pat. Nos. 5,247,190; 5,514,878 and 5,672,678). PLEDs have an advantage in terms of device fabrication as a printing methodology may be adopted for soluble polymer materials. Solution deposition of polymer material is a useful method to reduce the manufacturing cost for displays and light sources.
However, the problem associated with PLEDs is that the quantum efficiency and device lifetime are poor relative to SMOLEDs.
Polymer materials are usually synthesized by polymerisation of monomers of one or of several kinds and the resulting polymer materials tend to have a broad molecular weight distribution. PLEDs based on such polymers are difficult to manufacture due to solubility and reproducibility issues, which significantly affect the device operation lifetime, and have poor quantum efficiency. Also, quality control is difficult with PLEDs as the uniformity of the thin polymeric films, and the electronic properties of the materials, vary significantly depending on the particular method employed in forming the films and specific conditions used in the treating of the films.
Accordingly, novel organic polymeric luminescent materials in the production of PLEDs are needed, which are suitable for solution processing and which have narrow molecular weight distributions, good solubility, high thermal stability, high quantum efficiency, and good film uniformity.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common 15, general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.